How to Send E-Mail on Your iPhone
(Optional) Tap the field labeled Cc/Bcc/From:.
Doing so breaks them out into separate Cc:, Bcc:, and From: fields. The Cc/Bcc: label stands for carbon copy/blind carbon copy. If you haven’t used Bcc: before, it enables you to include a recipient on the message while hiding this fact from other recipients. Tap the respective Cc: or Bcc: field to type in names. Or tap the + that appears in those fields to add a contact. If you tap From instead, you can choose to send the message from any of your e-mail accounts on the fly, assuming, of course, you have more than one account.
If you start typing an e-mail address, e-mail addresses that match what you’ve typed appear in a list below the To or CC field. If the correct one is in the list, tap it to use it.